The overall goal of this project is in the spirit of Richard Feynman -- What I cannot create, I do not understand. Over the past decade many laboratories have reported new insights on synaptic transmission properties, based on electrophysiology, imaging, or biochemistry experiments. But the precise impact on synaptic properties of the various measured parameters such as molecular organization, mobility, or molecular interactions has remained elusive. Here we propose to overcome this problem through a synergy between the phenomenological descriptions of AMPAR organization based on super-resolution imaging techniques, the identification of the core of such organization with quantitative biochemistry, and quantitative biophysical modeling of synaptic transmission. The resulting model will deliver testable predictions of synaptic transmission properties that we will directly test with electrophysiological recordings. The ultimate result will be a reliable model based on brand new knowledge of synaptic organization and function at the nanoscale. The project will be divided into three Aims. In Aim 1 we will implement in an existing model three main modifications regarding newly available knowledge on AMPAR properties: (i) in situ constraints for the activation/inactivation kinetic rate constants of the tetrameric concerted opening model of AMPAR including the effect of AMPAR/TARP interaction on AMPAR gating properties; (ii) the tight organization of AMPAR in nanoclusters as reported recently by using super-resolution techniques; (iii) The lateral diffusion of AMPAR which has been measured with live single particle techniques. In Aim 2 we will measure the biochemical on/off rate and cross-affinity of the three main proteins responsible for AMPAR organization: PSD95, the TARPs and synGAP. At the end of this Aim, the model should be able to perfectly simulate synaptic transmission recorded at a neuron, both in term of kinetics, amplitude and variability, by taking into account the lateral mobility of AMPAR complex and PSD95 slot occupancy as a function of the determined affinity. Finally in Aim 3, we wfll validate the model and the hypothesis by modifying either the expression level of synGAP or the relative affinity of synGAP or TARP for PSD95, and then compare effect of such changes on AM PAR organization and dynamic properties and on synaptic transmission properties with the model predictions. RELEVANCE (See instructions): The proposed work involves study of the molecular mechanisms that control synaptic plasticity and their role in mental illness, a Strategic Research Priority of the NIMH. The work will help to clarify the function of the protein synGAP in CNS synapses and will impact Public Health as SynGAP has been found to be mutated in -1 % of children presenting a cognitive disability accompanied by autism and or epilepsy.